1. Field of the Invention
The invention relates generally to the field of ultrasound diagnostic probes and more specifically to the field of intraoperative ultrasound probes and acoustic signal transducers for ultrasound diagnostic applications.
2. Description of the Related Art
A previously known temperature probe has a low frequency magnetostriction transducer located on a plain wire (i.e., noncladded-core wire). The velocity of acoustic signals in the probe is a function of the temperature of the probe. Temperature is measured by measuring the time it takes for acoustic waves to travel from the magnetostriction transducer to the end of a calibrated temperature probe and back to the magnetostriction transducer. This device is described in "Ultrasonic Thin-Film Thermometry for Nuclear Applications" in ed. American Institute of Physics, 1982, page 1191.
A previously known magnetic field sensing device has two separate cladded-core fibers and couples light into one end of both fibers. One fiber has a magnetostriction transducer located somewhere in its middle. This transducer responds to a magnetic field by compressing the fiber and causing velocity changes and phase shifts in the light. The magnetic field is measured by comparing the phase shift of the light in one fiber with that in the other fiber, which is shielded from the magnetic field. This device is described in Fiber Optic Sensors, edited by Eric Udd, John Wiley & Sons, Inc. pages 382-390.
A previously known intraoperative ultrasound probe has piezoelectric transducers that the physician places directly on the artery during open heart surgery to locate the stenotic portion of an artery. The probe has miniature piezoelectric transducers configured as a phased array. These arrays operate at high frequencies, i.e., 10 to 20 MHz and require the application of a pulsed signal voltage to each piezoelectric element. These direct contact scanners are not in common use, except at the more advanced research hospitals, and they have many disadvantages. The piezoelectric transducer may emit leakage currents inside the body that can induce fibrillation when the probe images a coronary artery. Additionally, wires that connect the piezoelectric transducer to external circuitry inherently act as antennas and receive radio frequency interference present in a surgical facility.
Another disadvantage of previously known intraoperative probes is that the piezoelectric transducers configured in a phased array must be discarded after completion of a procedure to prevent transmission of disease. This is uneconomical because the piezoelectric transducers are difficult and expensive to make. It also discourages use of the most desirable transducers because they usually are more expensive. Generally, increasing the frequency of the acoustic signals improves the resolution capability of the transducer, but it also increases the expense because the operating frequency of piezoelectric transducers depends upon their thickness and the thinner the transducer, the more expensive it becomes to manufacture.
The more commonly used technique for detecting the stenotic portion of the artery during open heart surgery is palpation where surgeons literally feel with their fingers the segment of the artery that is harder than the rest. There is a widely acknowledged need to replace the palpation method with a device that is safe, economical and disposable.
For the reasons previously discussed, it would be advantageous to have an inexpensive intraoperative probe that images the arteries surrounding the heart without exposing the patient to the danger of leakage currents. Additionally, it would be desirable to have an inexpensive device for generating and coupling acoustic signals into a cladded-core acoustic waveguide that allows the acoustic waveguide to be disposable.